Solid State Bidirectional Light Sheet Having Vertical Orientation

ABSTRACT

A solid state, bidirectional light sheet and method of fabricating the sheet are disclosed. In one embodiment, bare LED chips have top and bottom electrodes, where the bottom electrode is a large reflective electrode. An array of LEDs (e.g., 500 LEDs) is sandwiched between at least two transparent substrates having conductors bonded to the electrodes without wires. Various ways to connect the LEDs in series are described along with various embodiments. The light sheets are formed to emit light from opposite surfaces of the light sheet to create a bidirectional light sheet. The light sheet may be suspended from a ceiling to be perpendicular to the ceiling, or the angles of the light sheet may be adjusted. The suspended light sheet may form a cylinder for uniform illumination of the floor and ceiling. Lenses may be formed in the light sheet to emit light at any peak intensity angle to achieve any light emission pattern.

FIELD OF INVENTION

This invention relates to solid state illumination and, in particular,to a substantially flat bidirectional light sheet containing lightemitting dies, such as light emitting diodes (LEDs), where the lightsheet is orientated at a non-parallel angle, such as vertically, withrespect to a ceiling.

BACKGROUND

High power LEDs are the conventional choice for general solid statelighting applications. Such high power white LEDs are extremely brightand can have luminous efficacies between 100 and 200 lumens/watt. Theinput power of a single high-power LED is typically greater than 0.5watt and may be greater than 10 watts. Such LEDs generate considerableheat since they are only about 1 mm² in area, so the required packagingis fairly complex and expensive. Although a bare high-power LED chiptypically costs well under $1.00 (e.g., $0.10), the packaged LEDtypically costs around $1.50-$3.00. This makes a high output (e.g.,3000+ lumens) solid state luminaire relatively expensive and not acommercially feasible alternative for a fluorescent light fixture,commonly used for general illumination. Further, the optics required toconvert the high brightness point sources into a substantiallyhomogeneous, broad angle emission for an office environment (where glarecontrol is important) is extremely challenging.

To greatly reduce the cost of a large area, high lumen output lightsource, it is known to sandwich an array of bare LED dice between areflective bottom sheet having conductors and a top transparent sheethaving conductors. The LEDs have top and bottom electrodes that contacta set of conductors. When the conductors on the sheets are energized,the LEDs emit light through only the transparent sheet. The light sheetmay be flexible.

Such prior art light sheets are not bidirectional.

It is also well known to provide a light emitting panel as a luminairefor general illumination, where the panel is oriented so that its lightemitting surface is parallel to a floor.

It may be desirable in certain environments to provide a cost-effectiveluminaire that generates lighting effects other than those of theabove-described prior art luminaires.

SUMMARY

Bidirectional light sheets and novel orientations of the light sheetsare described. The light sheets can be formed to have any dimensions,including narrow strips.

In one embodiment, an array of bare light emitting diode (LED) chips,having top electrodes and bottom electrodes, are sandwiched between twoor more substrates having conductors formed on their surfaces. LEDs withtop and bottom electrodes are typically referred to as vertical LEDs.The bottom electrode of commercially available vertical LEDs isreflective and covers the entire bottom surface of the LED. Therefore,the typical vertical LED emits light only from its top surface andsides. The top electrode is intended by the LED manufacturer to bebonded to a thin wire using ultrasonic bonding or other bondingtechnique.

The light sheets used in embodiments of the present invention employconductors on the substrates that electrically contact the LEDelectrodes without using wires. The conductors may connect any number ofLEDs in series and are ultimately connected to a power source. Inanother embodiment, wires may be used for the connections, addingconsiderable cost and complexity to the light sheet.

In one embodiment, the orientations of the vertical LEDs are alternatedso that the conductors on the substrates connect an anode of one LED tothe cathode of the adjacent LED for a series connection. In this way,the LEDs having one orientation emit light in one general direction, andLEDs having the opposite orientation emit light in the oppositedirection. Therefore, the light sheet emits bidirectional light.Reflectors (e.g., prisms) in the substrates may be used to direct anyside light toward the desired light output surface of the sheet.

In other embodiments, two light sheets are effectively affixedback-to-back, where the light sheets emit light in opposite directionsto form a bidirectional light sheet. A reflective sheet may be used asan intermediate layer between the opposing light sheets.

In one embodiment, control electronics may be located on or in anintermediate layer between the light sheets.

In an application of a bidirectional light sheet, the sheet (e.g., astrip) may be suspended from a ceiling so that it is orientatedvertically (i.e., perpendicular to the ceiling and floor). Optics may bemolded into the light emitting surfaces to angle the peak lightintensity downward (e.g., at 55 degrees relative to vertical) to avoidglare and to merge the light of one fixture with light from adjacentfixtures. Other ways of directing the light may also be used, such aslocating the LED chips in reflective cups or deep wells that emit acollimated beam of light at any selected angle. Portions of the lightsheet, or another light sheet in the same fixture, may also be designedto direct light upward to reflect off the ceiling to achieve broadillumination. Any combinations of peak intensity angles may be achieved.

In one embodiment, a luminaire is created with a plurality of pivotablebidirectional light sheets so the user can customize the light emissionpattern. In another embodiment, the flexible light sheet may be formedas a cylinder and suspended from the ceiling to provide uniformillumination of the floor and ceiling. In another embodiment, the lightsheet may be formed as a truncated pyramid and suspended from theceiling.

Light emitting dies other than LEDs may also be used.

Other variations are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The below described drawings are presented to illustrate some possibleexamples of the invention.

FIG. 1 is a simplified perspective view of a portion of a bidirectionallight sheet, in accordance with one embodiment of the invention, showingsome light emitting areas.

FIG. 2 illustrates a series connection of LEDs in the light sheet ofFIG. 1.

FIG. 3 is a cross-sectional view along line 3-3 in FIG. 1 showing LEDsin opposite orientations being connected in series.

FIG. 4 is a cross-sectional view along line 3-3 in FIG. 1 showingback-to-back light sheets containing flip-chip LEDs connected in series.

FIG. 5 is a cross-sectional view along line 3-3 in FIG. 1 showingback-to-back light sheets containing vertical LEDs connected in series.

FIG. 6 illustrates a conductor connection in the light sheet of FIG. 5showing the series connection between adjacent LEDs.

FIG. 7 is a perspective view of any of the bidirectional light sheetsbeing orientated approximately perpendicular to a ceiling and emittinglight at a variety of peak intensity angles.

FIG. 8 is a bottom up view of a luminaire containing a plurality of thebidirectional light sheets and adjustable to emit light at a variety ofpeak intensity angles.

FIG. 9 is a side view of the luminaire of FIG. 8.

FIG. 10 is a perspective view of a bidirectional light sheet that isbent to form a cylinder, where the cylinder is suspended from a ceiling.

FIG. 11 illustrates two curved bidirectional light sheets that may beangled in any direction and curved to have any radius. The light sheetsmay be suspended from a ceiling.

FIG. 12A is a side view of bidirectional light sheets forming atruncated pyramid, shown suspended from a ceiling.

FIG. 12B is a bottom up view of the luminaire of FIG. 12A.

Elements that are the same or similar are labeled with the samenumerals.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of a portion of a light sheet 10, showing asimplified pseudo-random pattern of LED areas 12. The LED areas 12 mayinstead be in an ordered pattern. There may be 500 or more low powerLEDs in the light sheet 10 to generate the approximately 3700 lumens(per the DOE CALiPER benchmark test) needed to replace a standardfluorescent fixture typically found in offices.

The pseudo-random pattern may repeat around the light sheet 10 (only theportion within the dashed outline is shown). A pseudo-random pattern ispreferred over an ordered pattern since, if one or more LEDs fail orhave a poor electrical connection, its absence will be significantlyharder to notice.

In one embodiment, the light sheet 10 is generally formed of three mainlayers: a transparent bottom substrate 14 having an electrode andconductor pattern; an intermediate sheet 16 acting as a spacer andoptional reflector; and a transparent top substrate 18 having anelectrode and conductor pattern. In one embodiment, the LED chips areelectrically connected between electrodes on the bottom substrate 14 andelectrodes on the top substrate 18. The light sheet 10 is very thin,such as a few millimeters, and is flexible.

FIG. 2 illustrates a sample pattern of conductors 19 on the topsubstrate 18 and/or bottom substrate 14 that connect any number of LEDchips in series. In the example of FIG. 2, two groups ofseries-connected LEDs in the LED areas 12 are connected in parallel. Theparallel connection may be selected by a customizable interconnector 22external to the light sheet. The customizable interconnection of the LEDchips allows the drive voltage and current to be selected by thecustomer or be customized for a particular size of light sheet. Theremay be many strings of LED chips in the light sheet that are connectedtogether in series, parallel, or connected to different power supplies.

A DC or AC power supply 23 is shown connected to the connector 22. Aninput of the power supply 23 may be connected to the mains voltage. Ifthe voltage drop of an LED series string is sufficiently high, theseries string of LEDs may be driven by a rectified mains voltage (e.g.,120 VAC).

As shown in FIG. 3, to achieve a series connection of LED chips usingtop and bottom conductors, some LEDs chips 26 are mounted on the bottomsubstrate 14 with their anodes 27 connected to the bottom substrateelectrodes 28 and other LED chips 26 are mounted with their cathodes 30connected to the bottom substrate electrodes 28. Ideally, adjacent LEDchips are reversely mounted to simplify the series connection pattern.The conductors 19 between the electrodes then connects the LED chips inseries. A similar pattern of conductors 32 on the top substrate 18connects the cathodes of LED chips 26 to the anodes of adjacent LEDchips 26.

In another embodiment, it is also possible to connect the LED chips intwo anti-parallel series branches, or derivatives thereof, that willenable the LED chips to be driven directly from AC, such as directlyfrom the mains voltage.

Since the cathodes 30 of the LED chips 26 are typically large reflectorsthat cover the entire bottom surface of the LED chips, the light emittedfrom the oppositely orientated LED chips 26 will be in oppositedirections. Reflectors 36 molded into the substrates 14/18 orintermediate sheet 16 may be used to reflect side light toward theoutput surfaces of the light sheet.

If the LED chips 26 emit blue light, phosphor 38 may be deposited overthe light path to convert the blue light to white light, as shown by thelight rays 40. Phosphor may also be incorporated into an encapsulantthat fills the holes in the intermediate sheet 16 surrounding the LEDchips 26.

Additional details of the various bidirectional light sheets shownherein may be found in U.S. application Ser. No. 12/870,760, filed onAug. 27, 2010, entitled, Solid State Light Sheet for GeneralIllumination, by Louis Lerman et al., incorporated herein by reference.

FIG. 4 illustrates another bidirectional light sheet, where the LEDchips 44 are flip chips, with anode and cathode electrodes 46 on thebottom surface of the LED chips 44. One set of LED chips 44 aresandwiched between a top substrate 18 and a bottom substrate 14, andanother set of LED chips is sandwiched between the same bottom substrate18 and another substrate 48. Alternately, two light sheets may beseparately manufactured and laminated together back-to-back. A reflectorlayer may be positioned between the two sets of LED chips. The LED chipsin each set may be connected in any combination of series and parallel.

FIG. 5 illustrates another embodiment of a bidirectional light sheet,where the top substrate 18 and bottom substrate 14 have conductors 50and 52 that overlap when the substrates are laminated together to form aseries connection between LED chips 26. Two light sheets are laminatedtogether with a reflective layer 53 between them to cause light to beemitted bidirectionally from the back-to-back light sheets.

FIG. 6 is a top down view of the light sheet portion of FIG. 5 showingthe overlapping conductors 50 and 52 connecting the LED chips 26 inseries.

The substrate electrodes over the LED chip anodes may by transparentconductors, such as ITO (indium-doped tin oxide) or ATO (antimony-dopedtin oxide) layers, to avoid blocking light.

The intermediate layer between the sets of LED chips may include controlelectronics and/or cross-over conductors for interconnecting the LEDchips and controlling brightness.

FIG. 7 illustrates any of the bidirectional light sheets being suspendedfrom a ceiling 60 by wires 61 and orientated approximately perpendicularto the ceiling 60. The wires 61 may conduct a low DC voltage (e.g., 24volts DC) to the LED chips or may supply a mains voltage to a powerconverter in the luminaire. The light sheets are shown emitting light 62at a variety of peak intensity angles. Lenses 63 may be molded in thetransparent surfaces of any of the light sheets to direct the peakintensity at any angle. The lenses may be Fresnel lenses, elongatedgrooved lenses, or other lens shapes to achieve the desired lightemission angles. Other ways of directing the light may also be used inany of the embodiments, such as locating the LED chips in reflectivecups or deep wells that emit a collimated beam of light at any selectedangle. This can be done by angling the cups or shaping the cups.

In FIG. 7, two, bidirectional light sheets 64 and 66 are mountedtogether in the same luminaire, where the light sheet 64 has lenses thatgenerally direct light downward, and the light sheet 66 has lenses thatgenerally direct light upward to reflect off the ceiling 60. Light fromadjacent, identical luminaires merge across the floor and ceiling tocreate an overall smooth lighting effect. The luminaires may replacestandard fluorescent lamp troffers, yet not require any space above theceiling. This enables the luminaires to be used where the ceiling is nota drop down ceiling.

The light angles coming from both sides of the light sheet may be mirrorimages for symmetry or may be asymmetrical.

Instead of a flat light sheet, the light sheet may be bent to form anarc or other shape, depending on the desired emission pattern.

The light sheet may be affixed to the ceiling at non-parallel anglesother than a vertical orientation, depending on the particular lighteffect desired. However, a symmetrical light emission for roomillumination will typically be desired.

In another embodiment, there are a variety of lenses in a single lightsheet to direct the light at two or more different angles. This may beused to create a very compact luminaire formed of one or more lightsheets.

Many other aesthetic light patterns may be generated from the verticalorientation of the bidirectional light sheets and the types of lensesformed in the light sheets.

FIG. 8 is a bottom up view, and FIG. 9 is a side view, of a luminairecontaining four bidirectional light sheets 70, which are adjustable toemit light at a variety of peak intensity angles. Each light sheet mayoutput light at a certain downward peak intensity angle, such as 55degrees relative to the nadir, or each light sheet may emit at adifferent peak intensity angle. The angles of the physical light sheets70 may be adjusted by pivoting 71 the light sheet around an axis. Forexample, one edge of each light sheet may be connected to a pivotingsupport on the luminaire base 72. The peak intensity light rays 74 fromthe four light sheets 70 are shown being at different angles. Any numberof light sheets 70 at any orientation (e.g., diagonal, parallel,perpendicular) may be used in the luminaire.

The bidirectionality of the flexible light sheet is very useful inhanging luminaires where it is desired to illuminate the ceiling as wellas the floor. Illuminating a ceiling creates a pleasant aesthetic effectand provides more uniform lighting throughout the room. FIGS. 10-12Billustrate additional luminaires that reflect light off the ceiling.

FIG. 10 is a perspective view of a bidirectional light sheet 78 that isbent to form a cylinder, where the cylinder is suspended from a ceiling80. The flexible light sheet 78 may be supported along its edges by aplastic cylindrical frame that is suspended from the ceiling 80 by wires82. The curvature of the light sheet 78 causes light to be evenlyemitted 360 degrees around a central axis. The peak intensity of lightmay be directed downward to avoid glare by lenses or other opticalmeans. In one embodiment, the peak intensity is at 55 degrees relativeto the nadir. The light emitted from the inside surface of the cylinderis both directed upward to reflect off the ceiling 80 and downward toavoid any dark spot under the luminaire. Angled light rays 84 are shownbeing emitted from the outer surface of the light sheet 78. The outersurface may also emit a percentage of the light toward the ceiling 80for more uniform illumination of the ceiling 80. An angled light ray 86is shown being emitted from the inside surface of the light sheet 78 andreflected off the ceiling 80 to avoid a dark spot above the luminaire,and downward light rays 88 are shown being emitted from the insidesurface of the light sheet 78 to avoid a dark spot under the luminaire.

FIG. 11 illustrates two curved bidirectional light sheets 90 and 92 thatmay be angled in any direction and curved to have any radius. The lightsheets 90/92 may be suspended from a ceiling as in FIG. 10. The lightsheets 90/92 may each be supported by a frame to allow each to beindependently tilted and pivoted around a central axis. Since the light94 emitted by each bidirectional light sheet 90/92 is asymmetrical,virtually any light pattern may be created by changing the angles anddirections of the light sheets 90/92.

FIG. 12A is a side view of bidirectional light sheets 96 forming atruncated pyramid, shown suspended from a ceiling 80. The light sheets96 are directed at a downward angle, such as at a 55 degree angle, todirect light 98 downward. This provides 360 degree coverage of thefloor. To avoid any dark spot above the luminaire and to illuminate theceiling well beyond the area of the light sheets 96, the inside surfacesof the light sheets 96 direct light 100 toward the ceiling 80. A lightsheet 96 may form the flat bottom surface of the luminaire, or thebottom may be open for increased air circulation.

FIG. 12B is a bottom up view of the luminaire of FIG. 12A. The lightsheets 96 may be at any angle, such as to minimize glare. Lenses in thelight sheet surfaces may be used to direct the light emission.

Other uses of a non-parallel oriented bidirectional light sheet are alsoenvisioned.

The various features of all embodiments may be combined in anycombination.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects and, therefore, the appended claims areto encompass within their scope all changes and modifications that fallwithin the true spirit and scope of the invention.

1-20. (canceled)
 21. A lighting device comprising: two or morebidirectional light sheets, each of the bidirectional light sheetshaving opposing first and second light emitting surfaces; and a planarbase, wherein each of the two or more bidirectional light sheets has anedge affixed to the planar base, such that the first and second lightemitting surfaces of each of the bidirectional light sheets form anangle different from zero with the planar base.